package com.feng.gaoerfu.view;

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import android.content.Context;
import android.content.res.TypedArray;
import android.database.DataSetObserver;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.os.Build;
import android.os.Parcel;
import android.os.Parcelable;
import android.os.SystemClock;
import android.support.v4.os.ParcelableCompat;
import android.support.v4.os.ParcelableCompatCreatorCallbacks;
import android.support.v4.view.KeyEventCompat;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.VelocityTrackerCompat;
import android.support.v4.view.ViewCompat;
import android.support.v4.view.ViewConfigurationCompat;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.EdgeEffectCompat;
import android.util.AttributeSet;
import android.util.Log;
import android.view.FocusFinder;
import android.view.Gravity;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.SoundEffectConstants;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.accessibility.AccessibilityEvent;
import android.view.animation.Interpolator;
import android.widget.Scroller;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

/**
 * Layout manager that allows the user to flip left and right through pages of
 * data. You supply an implementation of a {@link PagerAdapter} to generate the
 * pages that the view shows.
 * 
 * <p>
 * Note this class is currently under early design and development. The API will
 * likely change in later updates of the compatibility library, requiring
 * changes to the source code of apps when they are compiled against the newer
 * version.
 * </p>
 * 
 * <p>
 * ViewPager is most often used in conjunction with {@link android.app.Fragment}
 * , which is a convenient way to supply and manage the lifecycle of each page.
 * There are standard adapters implemented for using fragments with the
 * ViewPager, which cover the most common use cases. These are
 * {@link android.support.v4.app.FragmentPagerAdapter},
 * {@link android.support.v4.app.FragmentStatePagerAdapter},
 * {@link android.support.v13.app.FragmentPagerAdapter}, and
 * {@link android.support.v13.app.FragmentStatePagerAdapter}; each of these
 * classes have simple code showing how to build a full user interface with
 * them.
 * 
 * <p>
 * Here is a more complicated example of ViewPager, using it in conjuction with
 * {@link android.app.ActionBar} tabs. You can find other examples of using
 * ViewPager in the API 4+ Support Demos and API 13+ Support Demos sample code.
 * 
 * {@sample
 * development/samples/Support13Demos/src/com/example/android/supportv13/app/
 * ActionBarTabsPager.java complete}
 */
public class LazyViewPager extends ViewGroup
{
	private static final String TAG						= "LazyViewPager";
	private static final boolean	DEBUG					= false;

	private static final boolean	USE_CACHE				= false;

	private static final int		DEFAULT_OFFSCREEN_PAGES	= 0;			// 预加载的数量
	private static final int		MAX_SETTLE_DURATION		= 600;			// ms
	private static final int		MIN_DISTANCE_FOR_FLING	= 25;			// dips

	private static final int[]		LAYOUT_ATTRS			= new int[] {
															android.R.attr.layout_gravity
															};

	static class ItemInfo
	{
		Object object;
		int		position;
		boolean	scrolling;
	}

	private static final Comparator<ItemInfo> COMPARATOR				= new Comparator<ItemInfo>() {
																			@Override
																			public int compare(ItemInfo lhs, ItemInfo rhs)
																			{
																				return lhs.position - rhs.position;
																			}
																		};

	private static final Interpolator sInterpolator			= new Interpolator() {
																			public float getInterpolation(float t)
																			{
																				t -= 1.0f;
																				return t * t * t * t * t + 1.0f;
																			}
																		};

	private final ArrayList<ItemInfo> mItems					= new ArrayList<ItemInfo>();

	private PagerAdapter mAdapter;
	private int									mCurItem;												// Index
																										// of
																										// currently
																										// displayed
																										// page.
	private int									mRestoredCurItem		= -1;
	private Parcelable mRestoredAdapterState	= null;
	private ClassLoader mRestoredClassLoader	= null;
	private Scroller mScroller;
	private PagerObserver						mObserver;

	private int									mPageMargin;
	private Drawable mMarginDrawable;
	private int									mTopPageBounds;
	private int									mBottomPageBounds;

	private int									mChildWidthMeasureSpec;
	private int									mChildHeightMeasureSpec;
	private boolean								mInLayout;

	private boolean								mScrollingCacheEnabled;

	private boolean								mPopulatePending;
	private boolean								mScrolling;
	private int									mOffscreenPageLimit		= DEFAULT_OFFSCREEN_PAGES;

	private boolean								mIsBeingDragged;
	private boolean								mIsUnableToDrag;
	private int									mTouchSlop;
	private float								mInitialMotionX;
	/**
	 * Position of the last motion event.
	 */
	private float								mLastMotionX;
	private float								mLastMotionY;
	/**
	 * ID of the active pointer. This is used to retain consistency during
	 * drags/flings if multiple pointers are used.
	 */
	private int									mActivePointerId		= INVALID_POINTER;
	/**
	 * Sentinel value for no current active pointer. Used by
	 * {@link #mActivePointerId}.
	 */
	private static final int					INVALID_POINTER			= -1;

	/**
	 * Determines speed during touch scrolling
	 */
	private VelocityTracker mVelocityTracker;
	private int									mMinimumVelocity;
	private int									mMaximumVelocity;
	private int									mFlingDistance;

	private boolean								mFakeDragging;
	private long								mFakeDragBeginTime;

	private EdgeEffectCompat mLeftEdge;
	private EdgeEffectCompat mRightEdge;

	private boolean								mFirstLayout			= true;
	private boolean								mCalledSuper;
	private int									mDecorChildCount;

	private OnPageChangeListener				mOnPageChangeListener;
	private OnPageChangeListener				mInternalPageChangeListener;
	private OnAdapterChangeListener				mAdapterChangeListener;

	/**
	 * Indicates that the pager is in an idle, settled state. The current page
	 * is fully in view and no animation is in progress.
	 */
	public static final int						SCROLL_STATE_IDLE		= 0;

	/**
	 * Indicates that the pager is currently being dragged by the user.
	 */
	public static final int						SCROLL_STATE_DRAGGING	= 1;

	/**
	 * Indicates that the pager is in the process of settling to a final
	 * position.
	 */
	public static final int						SCROLL_STATE_SETTLING	= 2;

	private int									mScrollState			= SCROLL_STATE_IDLE;

	/**
	 * Callback interface for responding to changing state of the selected page.
	 */
	public interface OnPageChangeListener
	{

		/**
		 * This method will be invoked when the current page is scrolled, either
		 * as part of a programmatically initiated smooth scroll or a user
		 * initiated touch scroll.
		 * 
		 * @param position
		 *            Position index of the first page currently being
		 *            displayed. Page position+1 will be visible if
		 *            positionOffset is nonzero.
		 * @param positionOffset
		 *            Value from [0, 1) indicating the offset from the page at
		 *            position.
		 * @param positionOffsetPixels
		 *            Value in pixels indicating the offset from position.
		 */
		public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels);

		/**
		 * This method will be invoked when a new page becomes selected.
		 * Animation is not necessarily complete.
		 * 
		 * @param position
		 *            Position index of the new selected page.
		 */
		public void onPageSelected(int position);

		/**
		 * Called when the scroll state changes. Useful for discovering when the
		 * user begins dragging, when the pager is automatically settling to the
		 * current page, or when it is fully stopped/idle.
		 * 
		 * @param state
		 *            The new scroll state.
		 * @see ViewPager#SCROLL_STATE_IDLE
		 * @see ViewPager#SCROLL_STATE_DRAGGING
		 * @see ViewPager#SCROLL_STATE_SETTLING
		 */
		public void onPageScrollStateChanged(int state);
	}

	/**
	 * Simple implementation of the {@link OnPageChangeListener} interface with
	 * stub implementations of each method. Extend this if you do not intend to
	 * override every method of {@link OnPageChangeListener}.
	 */
	public static class SimpleOnPageChangeListener implements OnPageChangeListener
	{
		@Override
		public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels)
		{
			// This space for rent
		}

		@Override
		public void onPageSelected(int position)
		{
			// This space for rent
		}

		@Override
		public void onPageScrollStateChanged(int state)
		{
			// This space for rent
		}
	}

	/**
	 * Used internally to monitor when adapters are switched.
	 */
	interface OnAdapterChangeListener
	{
		public void onAdapterChanged(PagerAdapter oldAdapter, PagerAdapter newAdapter);
	}

	/**
	 * Used internally to tag special types of child views that should be added
	 * as pager decorations by default.
	 */
	interface Decor
	{
	}

	public LazyViewPager(Context context) {
		super(context);
		initViewPager();
	}

	public LazyViewPager(Context context, AttributeSet attrs) {
		super(context, attrs);
		initViewPager();
	}

	void initViewPager()
	{
		setWillNotDraw(false);
		setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
		setFocusable(true);
		final Context context = getContext();
		mScroller = new Scroller(context, sInterpolator);
		final ViewConfiguration configuration = ViewConfiguration.get(context);
		mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration);
		mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
		mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
		mLeftEdge = new EdgeEffectCompat(context);
		mRightEdge = new EdgeEffectCompat(context);

		final float density = context.getResources().getDisplayMetrics().density;
		mFlingDistance = (int) (MIN_DISTANCE_FOR_FLING * density);
	}

	private void setScrollState(int newState)
	{
		if (mScrollState == newState) { return; }

		mScrollState = newState;
		if (mOnPageChangeListener != null)
		{
			mOnPageChangeListener.onPageScrollStateChanged(newState);
		}
	}

	/**
	 * Set a PagerAdapter that will supply views for this pager as needed.
	 * 
	 * @param adapter
	 *            Adapter to use
	 */
	public void setAdapter(PagerAdapter adapter)
	{
		if (mAdapter != null)
		{
			// mAdapter.unregisterDataSetObserver(mObserver);
			mAdapter.startUpdate(this);
			for (int i = 0; i < mItems.size(); i++)
			{
				final ItemInfo ii = mItems.get(i);
				mAdapter.destroyItem(this, ii.position, ii.object);
			}
			mAdapter.finishUpdate(this);
			mItems.clear();
			removeNonDecorViews();
			mCurItem = 0;
			scrollTo(0, 0);
		}

		final PagerAdapter oldAdapter = mAdapter;
		mAdapter = adapter;

		if (mAdapter != null)
		{
			if (mObserver == null)
			{
				mObserver = new PagerObserver();
			}
			// mAdapter.registerDataSetObserver(mObserver);
			mPopulatePending = false;
			if (mRestoredCurItem >= 0)
			{
				mAdapter.restoreState(mRestoredAdapterState, mRestoredClassLoader);
				setCurrentItemInternal(mRestoredCurItem, false, true);
				mRestoredCurItem = -1;
				mRestoredAdapterState = null;
				mRestoredClassLoader = null;
			}
			else
			{
				populate();
			}
		}

		if (mAdapterChangeListener != null && oldAdapter != adapter)
		{
			mAdapterChangeListener.onAdapterChanged(oldAdapter, adapter);
		}
	}

	private void removeNonDecorViews()
	{
		for (int i = 0; i < getChildCount(); i++)
		{
			final View child = getChildAt(i);
			final LayoutParams lp = (LayoutParams) child.getLayoutParams();
			if (!lp.isDecor)
			{
				removeViewAt(i);
				i--;
			}
		}
	}

	/**
	 * Retrieve the current adapter supplying pages.
	 * 
	 * @return The currently registered PagerAdapter
	 */
	public PagerAdapter getAdapter()
	{
		return mAdapter;
	}

	void setOnAdapterChangeListener(OnAdapterChangeListener listener)
	{
		mAdapterChangeListener = listener;
	}

	/**
	 * Set the currently selected page. If the ViewPager has already been
	 * through its first layout there will be a smooth animated transition
	 * between the current item and the specified item.
	 * 
	 * @param item
	 *            Item index to select
	 */
	public void setCurrentItem(int item)
	{
		mPopulatePending = false;
		setCurrentItemInternal(item, !mFirstLayout, false);
	}

	/**
	 * Set the currently selected page.
	 * 
	 * @param item
	 *            Item index to select
	 * @param smoothScroll
	 *            True to smoothly scroll to the new item, false to transition
	 *            immediately
	 */
	public void setCurrentItem(int item, boolean smoothScroll)
	{
		mPopulatePending = false;
		setCurrentItemInternal(item, smoothScroll, false);
	}

	public int getCurrentItem()
	{
		return mCurItem;
	}

	void setCurrentItemInternal(int item, boolean smoothScroll, boolean always)
	{
		setCurrentItemInternal(item, smoothScroll, always, 0);
	}

	void setCurrentItemInternal(int item, boolean smoothScroll, boolean always, int velocity)
	{
		if (mAdapter == null || mAdapter.getCount() <= 0)
		{
			setScrollingCacheEnabled(false);
			return;
		}
		if (!always && mCurItem == item && mItems.size() != 0)
		{
			setScrollingCacheEnabled(false);
			return;
		}
		if (item < 0)
		{
			item = 0;
		}
		else if (item >= mAdapter.getCount())
		{
			item = mAdapter.getCount() - 1;
		}
		final int pageLimit = mOffscreenPageLimit;
		if (item > (mCurItem + pageLimit) || item < (mCurItem - pageLimit))
		{
			// We are doing a jump by more than one page. To avoid
			// glitches, we want to keep all current pages in the view
			// until the scroll ends.
			for (int i = 0; i < mItems.size(); i++)
			{
				mItems.get(i).scrolling = true;
			}
		}
		final boolean dispatchSelected = mCurItem != item;
		mCurItem = item;
		populate();
		final int destX = (getWidth() + mPageMargin) * item;
		if (smoothScroll)
		{
			smoothScrollTo(destX, 0, velocity);
			if (dispatchSelected && mOnPageChangeListener != null)
			{
				mOnPageChangeListener.onPageSelected(item);
			}
			if (dispatchSelected && mInternalPageChangeListener != null)
			{
				mInternalPageChangeListener.onPageSelected(item);
			}
		}
		else
		{
			if (dispatchSelected && mOnPageChangeListener != null)
			{
				mOnPageChangeListener.onPageSelected(item);
			}
			if (dispatchSelected && mInternalPageChangeListener != null)
			{
				mInternalPageChangeListener.onPageSelected(item);
			}
			completeScroll();
			scrollTo(destX, 0);
		}
	}

	/**
	 * Set a listener that will be invoked whenever the page changes or is
	 * incrementally scrolled. See {@link OnPageChangeListener}.
	 * 
	 * @param listener
	 *            Listener to set
	 */
	public void setOnPageChangeListener(OnPageChangeListener listener)
	{
		mOnPageChangeListener = listener;
	}

	/**
	 * Set a separate OnPageChangeListener for internal use by the support
	 * library.
	 * 
	 * @param listener
	 *            Listener to set
	 * @return The old listener that was set, if any.
	 */
	OnPageChangeListener setInternalPageChangeListener(OnPageChangeListener listener)
	{
		OnPageChangeListener oldListener = mInternalPageChangeListener;
		mInternalPageChangeListener = listener;
		return oldListener;
	}

	/**
	 * Returns the number of pages that will be retained to either side of the
	 * current page in the view hierarchy in an idle state. Defaults to 1.
	 * 
	 * @return How many pages will be kept offscreen on either side
	 * @see #setOffscreenPageLimit(int)
	 */
	public int getOffscreenPageLimit()
	{
		return mOffscreenPageLimit;
	}

	/**
	 * Set the number of pages that should be retained to either side of the
	 * current page in the view hierarchy in an idle state. Pages beyond this
	 * limit will be recreated from the adapter when needed.
	 * 
	 * <p>
	 * This is offered as an optimization. If you know in advance the number of
	 * pages you will need to support or have lazy-loading mechanisms in place
	 * on your pages, tweaking this setting can have benefits in perceived
	 * smoothness of paging animations and interaction. If you have a small
	 * number of pages (3-4) that you can keep active all at once, less time
	 * will be spent in layout for newly created view subtrees as the user pages
	 * back and forth.
	 * </p>
	 * 
	 * <p>
	 * You should keep this limit low, especially if your pages have complex
	 * layouts. This setting defaults to 1.
	 * </p>
	 * 
	 * @param limit
	 *            How many pages will be kept offscreen in an idle state.
	 */
	public void setOffscreenPageLimit(int limit)
	{
		if (limit < DEFAULT_OFFSCREEN_PAGES)
		{
			Log.w(TAG, "Requested offscreen page limit " + limit + " too small; defaulting to " +
						DEFAULT_OFFSCREEN_PAGES);
			limit = DEFAULT_OFFSCREEN_PAGES;
		}
		if (limit != mOffscreenPageLimit)
		{
			mOffscreenPageLimit = limit;
			populate();
		}
	}

	/**
	 * Set the margin between pages.
	 * 
	 * @param marginPixels
	 *            Distance between adjacent pages in pixels
	 * @see #getPageMargin()
	 * @see #setPageMarginDrawable(Drawable)
	 * @see #setPageMarginDrawable(int)
	 */
	public void setPageMargin(int marginPixels)
	{
		final int oldMargin = mPageMargin;
		mPageMargin = marginPixels;

		final int width = getWidth();
		recomputeScrollPosition(width, width, marginPixels, oldMargin);

		requestLayout();
	}

	/**
	 * Return the margin between pages.
	 * 
	 * @return The size of the margin in pixels
	 */
	public int getPageMargin()
	{
		return mPageMargin;
	}

	/**
	 * Set a drawable that will be used to fill the margin between pages.
	 * 
	 * @param d
	 *            Drawable to display between pages
	 */
	public void setPageMarginDrawable(Drawable d)
	{
		mMarginDrawable = d;
		if (d != null) refreshDrawableState();
		setWillNotDraw(d == null);
		invalidate();
	}

	/**
	 * Set a drawable that will be used to fill the margin between pages.
	 * 
	 * @param resId
	 *            Resource ID of a drawable to display between pages
	 */
	public void setPageMarginDrawable(int resId)
	{
		setPageMarginDrawable(getContext().getResources().getDrawable(resId));
	}

	@Override
	protected boolean verifyDrawable(Drawable who)
	{
		return super.verifyDrawable(who) || who == mMarginDrawable;
	}

	@Override
	protected void drawableStateChanged()
	{
		super.drawableStateChanged();
		final Drawable d = mMarginDrawable;
		if (d != null && d.isStateful())
		{
			d.setState(getDrawableState());
		}
	}

	// We want the duration of the page snap animation to be influenced by the
	// distance that
	// the screen has to travel, however, we don't want this duration to be
	// effected in a
	// purely linear fashion. Instead, we use this method to moderate the effect
	// that the distance
	// of travel has on the overall snap duration.
	float distanceInfluenceForSnapDuration(float f)
	{
		f -= 0.5f; // center the values about 0.
		f *= 0.3f * Math.PI / 2.0f;
		return (float) Math.sin(f);
	}

	/**
	 * Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
	 * 
	 * @param x
	 *            the number of pixels to scroll by on the X axis
	 * @param y
	 *            the number of pixels to scroll by on the Y axis
	 */
	void smoothScrollTo(int x, int y)
	{
		smoothScrollTo(x, y, 0);
	}

	/**
	 * Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
	 * 
	 * @param x
	 *            the number of pixels to scroll by on the X axis
	 * @param y
	 *            the number of pixels to scroll by on the Y axis
	 * @param velocity
	 *            the velocity associated with a fling, if applicable. (0
	 *            otherwise)
	 */
	void smoothScrollTo(int x, int y, int velocity)
	{
		if (getChildCount() == 0)
		{
			// Nothing to do.
			setScrollingCacheEnabled(false);
			return;
		}
		int sx = getScrollX();
		int sy = getScrollY();
		int dx = x - sx;
		int dy = y - sy;
		if (dx == 0 && dy == 0)
		{
			completeScroll();
			setScrollState(SCROLL_STATE_IDLE);
			return;
		}

		setScrollingCacheEnabled(true);
		mScrolling = true;
		setScrollState(SCROLL_STATE_SETTLING);

		final int width = getWidth();
		final int halfWidth = width / 2;
		final float distanceRatio = Math.min(1f, 1.0f * Math.abs(dx) / width);
		final float distance = halfWidth + halfWidth *
								distanceInfluenceForSnapDuration(distanceRatio);

		int duration = 0;
		velocity = Math.abs(velocity);
		if (velocity > 0)
		{
			duration = 4 * Math.round(1000 * Math.abs(distance / velocity));
		}
		else
		{
			final float pageDelta = (float) Math.abs(dx) / (width + mPageMargin);
			duration = (int) ((pageDelta + 1) * 100);
		}
		duration = Math.min(duration, MAX_SETTLE_DURATION);

		mScroller.startScroll(sx, sy, dx, dy, duration);
		invalidate();
	}

	void addNewItem(int position, int index)
	{
		ItemInfo ii = new ItemInfo();
		ii.position = position;
		ii.object = mAdapter.instantiateItem(this, position);
		if (index < 0)
		{
			mItems.add(ii);
		}
		else
		{
			mItems.add(index, ii);
		}
	}

	void dataSetChanged()
	{
		// This method only gets called if our observer is attached, so mAdapter
		// is non-null.

		boolean needPopulate = mItems.size() < 3 && mItems.size() < mAdapter.getCount();
		int newCurrItem = -1;

		boolean isUpdating = false;
		for (int i = 0; i < mItems.size(); i++)
		{
			final ItemInfo ii = mItems.get(i);
			final int newPos = mAdapter.getItemPosition(ii.object);

			if (newPos == PagerAdapter.POSITION_UNCHANGED)
			{
				continue;
			}

			if (newPos == PagerAdapter.POSITION_NONE)
			{
				mItems.remove(i);
				i--;

				if (!isUpdating)
				{
					mAdapter.startUpdate(this);
					isUpdating = true;
				}

				mAdapter.destroyItem(this, ii.position, ii.object);
				needPopulate = true;

				if (mCurItem == ii.position)
				{
					// Keep the current item in the valid range
					newCurrItem = Math.max(0, Math.min(mCurItem, mAdapter.getCount() - 1));
				}
				continue;
			}

			if (ii.position != newPos)
			{
				if (ii.position == mCurItem)
				{
					// Our current item changed position. Follow it.
					newCurrItem = newPos;
				}

				ii.position = newPos;
				needPopulate = true;
			}
		}

		if (isUpdating)
		{
			mAdapter.finishUpdate(this);
		}

		Collections.sort(mItems, COMPARATOR);

		if (newCurrItem >= 0)
		{
			// TODO This currently causes a jump.
			setCurrentItemInternal(newCurrItem, false, true);
			needPopulate = true;
		}
		if (needPopulate)
		{
			populate();
			requestLayout();
		}
	}

	void populate()
	{
		if (mAdapter == null) { return; }

		// Bail now if we are waiting to populate. This is to hold off
		// on creating views from the time the user releases their finger to
		// fling to a new position until we have finished the scroll to
		// that position, avoiding glitches from happening at that point.
		if (mPopulatePending)
		{
			if (DEBUG) Log.i(TAG, "populate is pending, skipping for now...");
			return;
		}

		// Also, don't populate until we are attached to a window. This is to
		// avoid trying to populate before we have restored our view hierarchy
		// state and conflicting with what is restored.
		if (getWindowToken() == null) { return; }

		mAdapter.startUpdate(this);

		final int pageLimit = mOffscreenPageLimit;
		final int startPos = Math.max(0, mCurItem - pageLimit);
		final int N = mAdapter.getCount();
		final int endPos = Math.min(N - 1, mCurItem + pageLimit);

		if (DEBUG) Log.v(TAG, "populating: startPos=" + startPos + " endPos=" + endPos);

		// Add and remove pages in the existing list.
		int lastPos = -1;
		for (int i = 0; i < mItems.size(); i++)
		{
			ItemInfo ii = mItems.get(i);
			if ((ii.position < startPos || ii.position > endPos) && !ii.scrolling)
			{
				if (DEBUG) Log.i(TAG, "removing: " + ii.position + " @ " + i);
				mItems.remove(i);
				i--;
				mAdapter.destroyItem(this, ii.position, ii.object);
			}
			else if (lastPos < endPos && ii.position > startPos)
			{
				// The next item is outside of our range, but we have a gap
				// between it and the last item where we want to have a page
				// shown. Fill in the gap.
				lastPos++;
				if (lastPos < startPos)
				{
					lastPos = startPos;
				}
				while (lastPos <= endPos && lastPos < ii.position)
				{
					if (DEBUG) Log.i(TAG, "inserting: " + lastPos + " @ " + i);
					addNewItem(lastPos, i);
					lastPos++;
					i++;
				}
			}
			lastPos = ii.position;
		}

		// Add any new pages we need at the end.
		lastPos = mItems.size() > 0 ? mItems.get(mItems.size() - 1).position : -1;
		if (lastPos < endPos)
		{
			lastPos++;
			lastPos = lastPos > startPos ? lastPos : startPos;
			while (lastPos <= endPos)
			{
				if (DEBUG) Log.i(TAG, "appending: " + lastPos);
				addNewItem(lastPos, -1);
				lastPos++;
			}
		}

		if (DEBUG)
		{
			Log.i(TAG, "Current page list:");
			for (int i = 0; i < mItems.size(); i++)
			{
				Log.i(TAG, "#" + i + ": page " + mItems.get(i).position);
			}
		}

		ItemInfo curItem = null;
		for (int i = 0; i < mItems.size(); i++)
		{
			if (mItems.get(i).position == mCurItem)
			{
				curItem = mItems.get(i);
				break;
			}
		}
		mAdapter.setPrimaryItem(this, mCurItem, curItem != null ? curItem.object : null);

		mAdapter.finishUpdate(this);

		if (hasFocus())
		{
			View currentFocused = findFocus();
			ItemInfo ii = currentFocused != null ? infoForAnyChild(currentFocused) : null;
			if (ii == null || ii.position != mCurItem)
			{
				for (int i = 0; i < getChildCount(); i++)
				{
					View child = getChildAt(i);
					ii = infoForChild(child);
					if (ii != null && ii.position == mCurItem)
					{
						if (child.requestFocus(FOCUS_FORWARD))
						{
							break;
						}
					}
				}
			}
		}
	}

	/**
	 * This is the persistent state that is saved by ViewPager. Only needed if
	 * you are creating a sublass of ViewPager that must save its own state, in
	 * which case it should implement a subclass of this which contains that
	 * state.
	 */
	public static class SavedState extends BaseSavedState
	{
		int			position;
		Parcelable adapterState;
		ClassLoader loader;

		public SavedState(Parcelable superState) {
			super(superState);
		}

		@Override
		public void writeToParcel(Parcel out, int flags)
		{
			super.writeToParcel(out, flags);
			out.writeInt(position);
			out.writeParcelable(adapterState, flags);
		}

		@Override
		public String toString()
		{
			return "FragmentPager.SavedState{"
					+ Integer.toHexString(System.identityHashCode(this))
					+ " position=" + position + "}";
		}

		public static final Creator<SavedState> CREATOR	= ParcelableCompat.newCreator(new ParcelableCompatCreatorCallbacks<SavedState>() {
																		@Override
																		public SavedState createFromParcel(Parcel in, ClassLoader loader)
																		{
																			return new SavedState(in, loader);
																		}

																		@Override
																		public SavedState[] newArray(int size)
																		{
																			return new SavedState[size];
																		}
																	});

		SavedState(Parcel in, ClassLoader loader) {
			super(in);
			if (loader == null)
			{
				loader = getClass().getClassLoader();
			}
			position = in.readInt();
			adapterState = in.readParcelable(loader);
			this.loader = loader;
		}
	}

	@Override
	public Parcelable onSaveInstanceState()
	{
		Parcelable superState = super.onSaveInstanceState();
		SavedState ss = new SavedState(superState);
		ss.position = mCurItem;
		if (mAdapter != null)
		{
			ss.adapterState = mAdapter.saveState();
		}
		return ss;
	}

	@Override
	public void onRestoreInstanceState(Parcelable state)
	{
		if (!(state instanceof SavedState))
		{
			super.onRestoreInstanceState(state);
			return;
		}

		SavedState ss = (SavedState) state;
		super.onRestoreInstanceState(ss.getSuperState());

		if (mAdapter != null)
		{
			mAdapter.restoreState(ss.adapterState, ss.loader);
			setCurrentItemInternal(ss.position, false, true);
		}
		else
		{
			mRestoredCurItem = ss.position;
			mRestoredAdapterState = ss.adapterState;
			mRestoredClassLoader = ss.loader;
		}
	}

	@Override
	public void addView(View child, int index, ViewGroup.LayoutParams params)
	{
		if (!checkLayoutParams(params))
		{
			params = generateLayoutParams(params);
		}
		final LayoutParams lp = (LayoutParams) params;
		lp.isDecor |= child instanceof Decor;
		if (mInLayout)
		{
			if (lp != null && lp.isDecor) { throw new IllegalStateException("Cannot add pager decor view during layout"); }
			addViewInLayout(child, index, params);
			child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec);
		}
		else
		{
			super.addView(child, index, params);
		}

		if (USE_CACHE)
		{
			if (child.getVisibility() != GONE)
			{
				child.setDrawingCacheEnabled(mScrollingCacheEnabled);
			}
			else
			{
				child.setDrawingCacheEnabled(false);
			}
		}
	}

	ItemInfo infoForChild(View child)
	{
		for (int i = 0; i < mItems.size(); i++)
		{
			ItemInfo ii = mItems.get(i);
			if (mAdapter.isViewFromObject(child, ii.object)) { return ii; }
		}
		return null;
	}

	ItemInfo infoForAnyChild(View child)
	{
		ViewParent parent;
		while ((parent = child.getParent()) != this)
		{
			if (parent == null || !(parent instanceof View)) { return null; }
			child = (View) parent;
		}
		return infoForChild(child);
	}

	@Override
	protected void onAttachedToWindow()
	{
		super.onAttachedToWindow();
		mFirstLayout = true;
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
	{
		// For simple implementation, or internal size is always 0.
		// We depend on the container to specify the layout size of
		// our view. We can't really know what it is since we will be
		// adding and removing different arbitrary views and do not
		// want the layout to change as this happens.
		setMeasuredDimension(getDefaultSize(0, widthMeasureSpec),
								getDefaultSize(0, heightMeasureSpec));

		// Children are just made to fill our space.
		int childWidthSize = getMeasuredWidth() - getPaddingLeft() - getPaddingRight();
		int childHeightSize = getMeasuredHeight() - getPaddingTop() - getPaddingBottom();

		/*
		 * Make sure all children have been properly measured. Decor views
		 * first. Right now we cheat and make this less complicated by assuming
		 * decor views won't intersect. We will pin to edges based on gravity.
		 */
		int size = getChildCount();
		for (int i = 0; i < size; ++i)
		{
			final View child = getChildAt(i);
			if (child.getVisibility() != GONE)
			{
				final LayoutParams lp = (LayoutParams) child.getLayoutParams();
				if (lp != null && lp.isDecor)
				{
					final int hgrav = lp.gravity & Gravity.HORIZONTAL_GRAVITY_MASK;
					final int vgrav = lp.gravity & Gravity.VERTICAL_GRAVITY_MASK;
					Log.d(TAG, "gravity: " + lp.gravity + " hgrav: " + hgrav + " vgrav: " + vgrav);
					int widthMode = MeasureSpec.AT_MOST;
					int heightMode = MeasureSpec.AT_MOST;
					boolean consumeVertical = vgrav == Gravity.TOP || vgrav == Gravity.BOTTOM;
					boolean consumeHorizontal = hgrav == Gravity.LEFT || hgrav == Gravity.RIGHT;

					if (consumeVertical)
					{
						widthMode = MeasureSpec.EXACTLY;
					}
					else if (consumeHorizontal)
					{
						heightMode = MeasureSpec.EXACTLY;
					}

					final int widthSpec = MeasureSpec.makeMeasureSpec(childWidthSize, widthMode);
					final int heightSpec = MeasureSpec.makeMeasureSpec(childHeightSize, heightMode);
					child.measure(widthSpec, heightSpec);

					if (consumeVertical)
					{
						childHeightSize -= child.getMeasuredHeight();
					}
					else if (consumeHorizontal)
					{
						childWidthSize -= child.getMeasuredWidth();
					}
				}
			}
		}

		mChildWidthMeasureSpec = MeasureSpec.makeMeasureSpec(childWidthSize, MeasureSpec.EXACTLY);
		mChildHeightMeasureSpec = MeasureSpec.makeMeasureSpec(childHeightSize, MeasureSpec.EXACTLY);

		// Make sure we have created all fragments that we need to have shown.
		mInLayout = true;
		populate();
		mInLayout = false;

		// Page views next.
		size = getChildCount();
		for (int i = 0; i < size; ++i)
		{
			final View child = getChildAt(i);
			if (child.getVisibility() != GONE)
			{
				if (DEBUG) Log.v(TAG, "Measuring #" + i + " " + child
										+ ": " + mChildWidthMeasureSpec);

				final LayoutParams lp = (LayoutParams) child.getLayoutParams();
				if (lp == null || !lp.isDecor)
				{
					child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec);
				}
			}
		}
	}

	@Override
	protected void onSizeChanged(int w, int h, int oldw, int oldh)
	{
		super.onSizeChanged(w, h, oldw, oldh);

		// Make sure scroll position is set correctly.
		if (w != oldw)
		{
			recomputeScrollPosition(w, oldw, mPageMargin, mPageMargin);
		}
	}

	private void recomputeScrollPosition(int width, int oldWidth, int margin, int oldMargin)
	{
		final int widthWithMargin = width + margin;
		if (oldWidth > 0)
		{
			final int oldScrollPos = getScrollX();
			final int oldwwm = oldWidth + oldMargin;
			final int oldScrollItem = oldScrollPos / oldwwm;
			final float scrollOffset = (float) (oldScrollPos % oldwwm) / oldwwm;
			final int scrollPos = (int) ((oldScrollItem + scrollOffset) * widthWithMargin);
			scrollTo(scrollPos, getScrollY());
			if (!mScroller.isFinished())
			{
				// We now return to your regularly scheduled scroll, already in
				// progress.
				final int newDuration = mScroller.getDuration() - mScroller.timePassed();
				mScroller.startScroll(scrollPos, 0, mCurItem * widthWithMargin, 0, newDuration);
			}
		}
		else
		{
			int scrollPos = mCurItem * widthWithMargin;
			if (scrollPos != getScrollX())
			{
				completeScroll();
				scrollTo(scrollPos, getScrollY());
			}
		}
	}

	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b)
	{
		mInLayout = true;
		populate();
		mInLayout = false;

		final int count = getChildCount();
		int width = r - l;
		int height = b - t;
		int paddingLeft = getPaddingLeft();
		int paddingTop = getPaddingTop();
		int paddingRight = getPaddingRight();
		int paddingBottom = getPaddingBottom();
		final int scrollX = getScrollX();

		int decorCount = 0;

		for (int i = 0; i < count; i++)
		{
			final View child = getChildAt(i);
			if (child.getVisibility() != GONE)
			{
				final LayoutParams lp = (LayoutParams) child.getLayoutParams();
				ItemInfo ii;
				int childLeft = 0;
				int childTop = 0;
				if (lp.isDecor)
				{
					final int hgrav = lp.gravity & Gravity.HORIZONTAL_GRAVITY_MASK;
					final int vgrav = lp.gravity & Gravity.VERTICAL_GRAVITY_MASK;
					switch (hgrav)
					{
						default:
							childLeft = paddingLeft;
							break;
						case Gravity.LEFT:
							childLeft = paddingLeft;
							paddingLeft += child.getMeasuredWidth();
							break;
						case Gravity.CENTER_HORIZONTAL:
							childLeft = Math.max((width - child.getMeasuredWidth()) / 2,
													paddingLeft);
							break;
						case Gravity.RIGHT:
							childLeft = width - paddingRight - child.getMeasuredWidth();
							paddingRight += child.getMeasuredWidth();
							break;
					}
					switch (vgrav)
					{
						default:
							childTop = paddingTop;
							break;
						case Gravity.TOP:
							childTop = paddingTop;
							paddingTop += child.getMeasuredHeight();
							break;
						case Gravity.CENTER_VERTICAL:
							childTop = Math.max((height - child.getMeasuredHeight()) / 2,
												paddingTop);
							break;
						case Gravity.BOTTOM:
							childTop = height - paddingBottom - child.getMeasuredHeight();
							paddingBottom += child.getMeasuredHeight();
							break;
					}
					childLeft += scrollX;
					decorCount++;
					child.layout(childLeft, childTop,
									childLeft + child.getMeasuredWidth(),
									childTop + child.getMeasuredHeight());
				}
				else if ((ii = infoForChild(child)) != null)
				{
					int loff = (width + mPageMargin) * ii.position;
					childLeft = paddingLeft + loff;
					childTop = paddingTop;
					if (DEBUG) Log.v(TAG, "Positioning #" + i + " " + child + " f=" + ii.object
											+ ":" + childLeft + "," + childTop + " " + child.getMeasuredWidth()
											+ "x" + child.getMeasuredHeight());
					child.layout(childLeft, childTop,
									childLeft + child.getMeasuredWidth(),
									childTop + child.getMeasuredHeight());
				}
			}
		}
		mTopPageBounds = paddingTop;
		mBottomPageBounds = height - paddingBottom;
		mDecorChildCount = decorCount;
		mFirstLayout = false;
	}

	@Override
	public void computeScroll()
	{
		if (DEBUG) Log.i(TAG, "computeScroll: finished=" + mScroller.isFinished());
		if (!mScroller.isFinished())
		{
			if (mScroller.computeScrollOffset())
			{
				if (DEBUG) Log.i(TAG, "computeScroll: still scrolling");
				int oldX = getScrollX();
				int oldY = getScrollY();
				int x = mScroller.getCurrX();
				int y = mScroller.getCurrY();

				if (oldX != x || oldY != y)
				{
					scrollTo(x, y);
					pageScrolled(x);
				}

				// Keep on drawing until the animation has finished.
				invalidate();
				return;
			}
		}

		// Done with scroll, clean up state.
		completeScroll();
	}

	private void pageScrolled(int xpos)
	{
		final int widthWithMargin = getWidth() + mPageMargin;
		final int position = xpos / widthWithMargin;
		final int offsetPixels = xpos % widthWithMargin;
		final float offset = (float) offsetPixels / widthWithMargin;

		mCalledSuper = false;
		onPageScrolled(position, offset, offsetPixels);
		if (!mCalledSuper) { throw new IllegalStateException(
																"onPageScrolled did not call superclass implementation"); }
	}

	/**
	 * This method will be invoked when the current page is scrolled, either as
	 * part of a programmatically initiated smooth scroll or a user initiated
	 * touch scroll. If you override this method you must call through to the
	 * superclass implementation (e.g. super.onPageScrolled(position, offset,
	 * offsetPixels)) before onPageScrolled returns.
	 * 
	 * @param position
	 *            Position index of the first page currently being displayed.
	 *            Page position+1 will be visible if positionOffset is nonzero.
	 * @param offset
	 *            Value from [0, 1) indicating the offset from the page at
	 *            position.
	 * @param offsetPixels
	 *            Value in pixels indicating the offset from position.
	 */
	protected void onPageScrolled(int position, float offset, int offsetPixels)
	{
		// Offset any decor views if needed - keep them on-screen at all times.
		if (mDecorChildCount > 0)
		{
			final int scrollX = getScrollX();
			int paddingLeft = getPaddingLeft();
			int paddingRight = getPaddingRight();
			final int width = getWidth();
			final int childCount = getChildCount();
			for (int i = 0; i < childCount; i++)
			{
				final View child = getChildAt(i);
				final LayoutParams lp = (LayoutParams) child.getLayoutParams();
				if (!lp.isDecor) continue;

				final int hgrav = lp.gravity & Gravity.HORIZONTAL_GRAVITY_MASK;
				int childLeft = 0;
				switch (hgrav)
				{
					default:
						childLeft = paddingLeft;
						break;
					case Gravity.LEFT:
						childLeft = paddingLeft;
						paddingLeft += child.getWidth();
						break;
					case Gravity.CENTER_HORIZONTAL:
						childLeft = Math.max((width - child.getMeasuredWidth()) / 2,
												paddingLeft);
						break;
					case Gravity.RIGHT:
						childLeft = width - paddingRight - child.getMeasuredWidth();
						paddingRight += child.getMeasuredWidth();
						break;
				}
				childLeft += scrollX;

				final int childOffset = childLeft - child.getLeft();
				if (childOffset != 0)
				{
					child.offsetLeftAndRight(childOffset);
				}
			}
		}

		if (mOnPageChangeListener != null)
		{
			mOnPageChangeListener.onPageScrolled(position, offset, offsetPixels);
		}
		if (mInternalPageChangeListener != null)
		{
			mInternalPageChangeListener.onPageScrolled(position, offset, offsetPixels);
		}
		mCalledSuper = true;
	}

	private void completeScroll()
	{
		boolean needPopulate = mScrolling;
		if (needPopulate)
		{
			// Done with scroll, no longer want to cache view drawing.
			setScrollingCacheEnabled(false);
			mScroller.abortAnimation();
			int oldX = getScrollX();
			int oldY = getScrollY();
			int x = mScroller.getCurrX();
			int y = mScroller.getCurrY();
			if (oldX != x || oldY != y)
			{
				scrollTo(x, y);
			}
			setScrollState(SCROLL_STATE_IDLE);
		}
		mPopulatePending = false;
		mScrolling = false;
		for (int i = 0; i < mItems.size(); i++)
		{
			ItemInfo ii = mItems.get(i);
			if (ii.scrolling)
			{
				needPopulate = true;
				ii.scrolling = false;
			}
		}
		if (needPopulate)
		{
			populate();
		}
	}

	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev)
	{
		/*
		 * This method JUST determines whether we want to intercept the motion.
		 * If we return true, onMotionEvent will be called and we do the actual
		 * scrolling there.
		 */

		final int action = ev.getAction() & MotionEventCompat.ACTION_MASK;

		// Always take care of the touch gesture being complete.
		if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP)
		{
			// Release the drag.
			if (DEBUG) Log.v(TAG, "Intercept done!");
			mIsBeingDragged = false;
			mIsUnableToDrag = false;
			mActivePointerId = INVALID_POINTER;
			if (mVelocityTracker != null)
			{
				mVelocityTracker.recycle();
				mVelocityTracker = null;
			}
			return false;
		}

		// Nothing more to do here if we have decided whether or not we
		// are dragging.
		if (action != MotionEvent.ACTION_DOWN)
		{
			if (mIsBeingDragged)
			{
				if (DEBUG) Log.v(TAG, "Intercept returning true!");
				return true;
			}
			if (mIsUnableToDrag)
			{
				if (DEBUG) Log.v(TAG, "Intercept returning false!");
				return false;
			}
		}

		switch (action)
		{
			case MotionEvent.ACTION_MOVE:
			{
				/*
				 * mIsBeingDragged == false, otherwise the shortcut would have
				 * caught it. Check whether the user has moved far enough from
				 * his original down touch.
				 */

				/*
				 * Locally do absolute value. mLastMotionY is set to the y value
				 * of the down event.
				 */
				final int activePointerId = mActivePointerId;
				if (activePointerId == INVALID_POINTER)
				{
					// If we don't have a valid id, the touch down wasn't on
					// content.
					break;
				}

				final int pointerIndex = MotionEventCompat.findPointerIndex(ev, activePointerId);
				final float x = MotionEventCompat.getX(ev, pointerIndex);
				final float dx = x - mLastMotionX;
				final float xDiff = Math.abs(dx);
				final float y = MotionEventCompat.getY(ev, pointerIndex);
				final float yDiff = Math.abs(y - mLastMotionY);
				if (DEBUG) Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff);

				if (canScroll(this, false, (int) dx, (int) x, (int) y))
				{
					// Nested view has scrollable area under this point. Let it
					// be handled there.
					mInitialMotionX = mLastMotionX = x;
					mLastMotionY = y;
					return false;
				}
				if (xDiff > mTouchSlop && xDiff > yDiff)
				{
					if (DEBUG) Log.v(TAG, "Starting drag!");
					mIsBeingDragged = true;
					setScrollState(SCROLL_STATE_DRAGGING);
					mLastMotionX = x;
					setScrollingCacheEnabled(true);
				}
				else
				{
					if (yDiff > mTouchSlop)
					{
						// The finger has moved enough in the vertical
						// direction to be counted as a drag... abort
						// any attempt to drag horizontally, to work correctly
						// with children that have scrolling containers.
						if (DEBUG) Log.v(TAG, "Starting unable to drag!");
						mIsUnableToDrag = true;
					}
				}
				break;
			}

			case MotionEvent.ACTION_DOWN:
			{
				/*
				 * Remember location of down touch. ACTION_DOWN always refers to
				 * pointer index 0.
				 */
				mLastMotionX = mInitialMotionX = ev.getX();
				mLastMotionY = ev.getY();
				mActivePointerId = MotionEventCompat.getPointerId(ev, 0);

				if (mScrollState == SCROLL_STATE_SETTLING)
				{
					// Let the user 'catch' the pager as it animates.
					mIsBeingDragged = true;
					mIsUnableToDrag = false;
					setScrollState(SCROLL_STATE_DRAGGING);
				}
				else
				{
					completeScroll();
					mIsBeingDragged = false;
					mIsUnableToDrag = false;
				}

				if (DEBUG) Log.v(TAG, "Down at " + mLastMotionX + "," + mLastMotionY
										+ " mIsBeingDragged=" + mIsBeingDragged
										+ "mIsUnableToDrag=" + mIsUnableToDrag);
				break;
			}

			case MotionEventCompat.ACTION_POINTER_UP:
				onSecondaryPointerUp(ev);
				break;
		}

		if (!mIsBeingDragged)
		{
			// Track the velocity as long as we aren't dragging.
			// Once we start a real drag we will track in onTouchEvent.
			if (mVelocityTracker == null)
			{
				mVelocityTracker = VelocityTracker.obtain();
			}
			mVelocityTracker.addMovement(ev);
		}

		/*
		 * The only time we want to intercept motion events is if we are in the
		 * drag mode.
		 */
		return mIsBeingDragged;
	}

	@Override
	public boolean onTouchEvent(MotionEvent ev)
	{
		if (mFakeDragging)
		{
			// A fake drag is in progress already, ignore this real one
			// but still eat the touch events.
			// (It is likely that the user is multi-touching the screen.)
			return true;
		}

		if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0)
		{
			// Don't handle edge touches immediately -- they may actually belong
			// to one of our
			// descendants.
			return false;
		}

		if (mAdapter == null || mAdapter.getCount() == 0)
		{
			// Nothing to present or scroll; nothing to touch.
			return false;
		}

		if (mVelocityTracker == null)
		{
			mVelocityTracker = VelocityTracker.obtain();
		}
		mVelocityTracker.addMovement(ev);

		final int action = ev.getAction();
		boolean needsInvalidate = false;

		switch (action & MotionEventCompat.ACTION_MASK)
		{
			case MotionEvent.ACTION_DOWN:
			{
				/*
				 * If being flinged and user touches, stop the fling. isFinished
				 * will be false if being flinged.
				 */
				completeScroll();

				// Remember where the motion event started
				mLastMotionX = mInitialMotionX = ev.getX();
				mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
				break;
			}
			case MotionEvent.ACTION_MOVE:
				if (!mIsBeingDragged)
				{
					final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
					final float x = MotionEventCompat.getX(ev, pointerIndex);
					final float xDiff = Math.abs(x - mLastMotionX);
					final float y = MotionEventCompat.getY(ev, pointerIndex);
					final float yDiff = Math.abs(y - mLastMotionY);
					if (DEBUG) Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff);
					if (xDiff > mTouchSlop && xDiff > yDiff)
					{
						if (DEBUG) Log.v(TAG, "Starting drag!");
						mIsBeingDragged = true;
						mLastMotionX = x;
						setScrollState(SCROLL_STATE_DRAGGING);
						setScrollingCacheEnabled(true);
					}
				}
				if (mIsBeingDragged)
				{
					// Scroll to follow the motion event
					final int activePointerIndex = MotionEventCompat.findPointerIndex(
																						ev, mActivePointerId);
					final float x = MotionEventCompat.getX(ev, activePointerIndex);
					final float deltaX = mLastMotionX - x;
					mLastMotionX = x;
					float oldScrollX = getScrollX();
					float scrollX = oldScrollX + deltaX;
					final int width = getWidth();
					final int widthWithMargin = width + mPageMargin;

					final int lastItemIndex = mAdapter.getCount() - 1;
					final float leftBound = Math.max(0, (mCurItem - 1) * widthWithMargin);
					final float rightBound =
												Math.min(mCurItem + 1, lastItemIndex) * widthWithMargin;
					if (scrollX < leftBound)
					{
						if (leftBound == 0)
						{
							float over = -scrollX;
							needsInvalidate = mLeftEdge.onPull(over / width);
						}
						scrollX = leftBound;
					}
					else if (scrollX > rightBound)
					{
						if (rightBound == lastItemIndex * widthWithMargin)
						{
							float over = scrollX - rightBound;
							needsInvalidate = mRightEdge.onPull(over / width);
						}
						scrollX = rightBound;
					}
					// Don't lose the rounded component
					mLastMotionX += scrollX - (int) scrollX;
					scrollTo((int) scrollX, getScrollY());
					pageScrolled((int) scrollX);
				}
				break;
			case MotionEvent.ACTION_UP:
				if (mIsBeingDragged)
				{
					final VelocityTracker velocityTracker = mVelocityTracker;
					velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
					int initialVelocity = (int) VelocityTrackerCompat.getXVelocity(
																					velocityTracker, mActivePointerId);
					mPopulatePending = true;
					final int widthWithMargin = getWidth() + mPageMargin;
					final int scrollX = getScrollX();
					final int currentPage = scrollX / widthWithMargin;
					final float pageOffset = (float) (scrollX % widthWithMargin) / widthWithMargin;
					final int activePointerIndex =
													MotionEventCompat.findPointerIndex(ev, mActivePointerId);
					final float x = MotionEventCompat.getX(ev, activePointerIndex);
					final int totalDelta = (int) (x - mInitialMotionX);
					int nextPage = determineTargetPage(currentPage, pageOffset, initialVelocity,
														totalDelta);
					setCurrentItemInternal(nextPage, true, true, initialVelocity);

					mActivePointerId = INVALID_POINTER;
					endDrag();
					needsInvalidate = mLeftEdge.onRelease() | mRightEdge.onRelease();
				}
				break;
			case MotionEvent.ACTION_CANCEL:
				if (mIsBeingDragged)
				{
					setCurrentItemInternal(mCurItem, true, true);
					mActivePointerId = INVALID_POINTER;
					endDrag();
					needsInvalidate = mLeftEdge.onRelease() | mRightEdge.onRelease();
				}
				break;
			case MotionEventCompat.ACTION_POINTER_DOWN:
			{
				final int index = MotionEventCompat.getActionIndex(ev);
				final float x = MotionEventCompat.getX(ev, index);
				mLastMotionX = x;
				mActivePointerId = MotionEventCompat.getPointerId(ev, index);
				break;
			}
			case MotionEventCompat.ACTION_POINTER_UP:
				onSecondaryPointerUp(ev);
				mLastMotionX = MotionEventCompat.getX(ev,
														MotionEventCompat.findPointerIndex(ev, mActivePointerId));
				break;
		}
		if (needsInvalidate)
		{
			invalidate();
		}
		return true;
	}

	private int determineTargetPage(int currentPage, float pageOffset, int velocity, int deltaX)
	{
		int targetPage;
		if (Math.abs(deltaX) > mFlingDistance && Math.abs(velocity) > mMinimumVelocity)
		{
			targetPage = velocity > 0 ? currentPage : currentPage + 1;
		}
		else
		{
			targetPage = (int) (currentPage + pageOffset + 0.5f);
		}

		return targetPage;
	}

	@Override
	public void draw(Canvas canvas)
	{
		super.draw(canvas);
		boolean needsInvalidate = false;

		final int overScrollMode = ViewCompat.getOverScrollMode(this);
		if (overScrollMode == ViewCompat.OVER_SCROLL_ALWAYS ||
			(overScrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS &&
				mAdapter != null && mAdapter.getCount() > 1))
		{
			if (!mLeftEdge.isFinished())
			{
				final int restoreCount = canvas.save();
				final int height = getHeight() - getPaddingTop() - getPaddingBottom();

				canvas.rotate(270);
				canvas.translate(-height + getPaddingTop(), 0);
				mLeftEdge.setSize(height, getWidth());
				needsInvalidate |= mLeftEdge.draw(canvas);
				canvas.restoreToCount(restoreCount);
			}
			if (!mRightEdge.isFinished())
			{
				final int restoreCount = canvas.save();
				final int width = getWidth();
				final int height = getHeight() - getPaddingTop() - getPaddingBottom();
				final int itemCount = mAdapter != null ? mAdapter.getCount() : 1;

				canvas.rotate(90);
				canvas.translate(-getPaddingTop(),
									-itemCount * (width + mPageMargin) + mPageMargin);
				mRightEdge.setSize(height, width);
				needsInvalidate |= mRightEdge.draw(canvas);
				canvas.restoreToCount(restoreCount);
			}
		}
		else
		{
			mLeftEdge.finish();
			mRightEdge.finish();
		}

		if (needsInvalidate)
		{
			// Keep animating
			invalidate();
		}
	}

	@Override
	protected void onDraw(Canvas canvas)
	{
		super.onDraw(canvas);

		// Draw the margin drawable if needed.
		if (mPageMargin > 0 && mMarginDrawable != null)
		{
			final int scrollX = getScrollX();
			final int width = getWidth();
			final int offset = scrollX % (width + mPageMargin);
			if (offset != 0)
			{
				// Pages fit completely when settled; we only need to draw when
				// in between
				final int left = scrollX - offset + width;
				mMarginDrawable.setBounds(left, mTopPageBounds, left + mPageMargin,
											mBottomPageBounds);
				mMarginDrawable.draw(canvas);
			}
		}
	}

	/**
	 * Start a fake drag of the pager.
	 * 
	 * <p>
	 * A fake drag can be useful if you want to synchronize the motion of the
	 * ViewPager with the touch scrolling of another view, while still letting
	 * the ViewPager control the snapping motion and fling behavior. (e.g.
	 * parallax-scrolling tabs.) Call {@link #fakeDragBy(float)} to simulate the
	 * actual drag motion. Call {@link #endFakeDrag()} to complete the fake drag
	 * and fling as necessary.
	 * 
	 * <p>
	 * During a fake drag the ViewPager will ignore all touch events. If a real
	 * drag is already in progress, this method will return false.
	 * 
	 * @return true if the fake drag began successfully, false if it could not
	 *         be started.
	 * 
	 * @see #fakeDragBy(float)
	 * @see #endFakeDrag()
	 */
	public boolean beginFakeDrag()
	{
		if (mIsBeingDragged) { return false; }
		mFakeDragging = true;
		setScrollState(SCROLL_STATE_DRAGGING);
		mInitialMotionX = mLastMotionX = 0;
		if (mVelocityTracker == null)
		{
			mVelocityTracker = VelocityTracker.obtain();
		}
		else
		{
			mVelocityTracker.clear();
		}
		final long time = SystemClock.uptimeMillis();
		final MotionEvent ev = MotionEvent.obtain(time, time, MotionEvent.ACTION_DOWN, 0, 0, 0);
		mVelocityTracker.addMovement(ev);
		ev.recycle();
		mFakeDragBeginTime = time;
		return true;
	}

	/**
	 * End a fake drag of the pager.
	 * 
	 * @see #beginFakeDrag()
	 * @see #fakeDragBy(float)
	 */
	public void endFakeDrag()
	{
		if (!mFakeDragging) { throw new IllegalStateException("No fake drag in progress. Call beginFakeDrag first."); }

		final VelocityTracker velocityTracker = mVelocityTracker;
		velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
		int initialVelocity = (int) VelocityTrackerCompat.getYVelocity(
																		velocityTracker, mActivePointerId);
		mPopulatePending = true;
		final int totalDelta = (int) (mLastMotionX - mInitialMotionX);
		final int scrollX = getScrollX();
		final int widthWithMargin = getWidth() + mPageMargin;
		final int currentPage = scrollX / widthWithMargin;
		final float pageOffset = (float) (scrollX % widthWithMargin) / widthWithMargin;
		int nextPage = determineTargetPage(currentPage, pageOffset, initialVelocity, totalDelta);
		setCurrentItemInternal(nextPage, true, true, initialVelocity);
		endDrag();

		mFakeDragging = false;
	}

	/**
	 * Fake drag by an offset in pixels. You must have called
	 * {@link #beginFakeDrag()} first.
	 * 
	 * @param xOffset
	 *            Offset in pixels to drag by.
	 * @see #beginFakeDrag()
	 * @see #endFakeDrag()
	 */
	public void fakeDragBy(float xOffset)
	{
		if (!mFakeDragging) { throw new IllegalStateException("No fake drag in progress. Call beginFakeDrag first."); }

		mLastMotionX += xOffset;
		float scrollX = getScrollX() - xOffset;
		final int width = getWidth();
		final int widthWithMargin = width + mPageMargin;

		final float leftBound = Math.max(0, (mCurItem - 1) * widthWithMargin);
		final float rightBound =
									Math.min(mCurItem + 1, mAdapter.getCount() - 1) * widthWithMargin;
		if (scrollX < leftBound)
		{
			scrollX = leftBound;
		}
		else if (scrollX > rightBound)
		{
			scrollX = rightBound;
		}
		// Don't lose the rounded component
		mLastMotionX += scrollX - (int) scrollX;
		scrollTo((int) scrollX, getScrollY());
		pageScrolled((int) scrollX);

		// Synthesize an event for the VelocityTracker.
		final long time = SystemClock.uptimeMillis();
		final MotionEvent ev = MotionEvent.obtain(mFakeDragBeginTime, time, MotionEvent.ACTION_MOVE,
													mLastMotionX, 0, 0);
		mVelocityTracker.addMovement(ev);
		ev.recycle();
	}

	/**
	 * Returns true if a fake drag is in progress.
	 * 
	 * @return true if currently in a fake drag, false otherwise.
	 * 
	 * @see #beginFakeDrag()
	 * @see #fakeDragBy(float)
	 * @see #endFakeDrag()
	 */
	public boolean isFakeDragging()
	{
		return mFakeDragging;
	}

	private void onSecondaryPointerUp(MotionEvent ev)
	{
		final int pointerIndex = MotionEventCompat.getActionIndex(ev);
		final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex);
		if (pointerId == mActivePointerId)
		{
			// This was our active pointer going up. Choose a new
			// active pointer and adjust accordingly.
			final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
			mLastMotionX = MotionEventCompat.getX(ev, newPointerIndex);
			mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex);
			if (mVelocityTracker != null)
			{
				mVelocityTracker.clear();
			}
		}
	}

	private void endDrag()
	{
		mIsBeingDragged = false;
		mIsUnableToDrag = false;

		if (mVelocityTracker != null)
		{
			mVelocityTracker.recycle();
			mVelocityTracker = null;
		}
	}

	private void setScrollingCacheEnabled(boolean enabled)
	{
		if (mScrollingCacheEnabled != enabled)
		{
			mScrollingCacheEnabled = enabled;
			if (USE_CACHE)
			{
				final int size = getChildCount();
				for (int i = 0; i < size; ++i)
				{
					final View child = getChildAt(i);
					if (child.getVisibility() != GONE)
					{
						child.setDrawingCacheEnabled(enabled);
					}
				}
			}
		}
	}

	/**
	 * Tests scrollability within child views of v given a delta of dx.
	 * 
	 * @param v
	 *            View to test for horizontal scrollability
	 * @param checkV
	 *            Whether the view v passed should itself be checked for
	 *            scrollability (true), or just its children (false).
	 * @param dx
	 *            Delta scrolled in pixels
	 * @param x
	 *            X coordinate of the active touch point
	 * @param y
	 *            Y coordinate of the active touch point
	 * @return true if child views of v can be scrolled by delta of dx.
	 */
	protected boolean canScroll(View v, boolean checkV, int dx, int x, int y)
	{
		if (v instanceof ViewGroup)
		{
			final ViewGroup group = (ViewGroup) v;
			final int scrollX = v.getScrollX();
			final int scrollY = v.getScrollY();
			final int count = group.getChildCount();
			// Count backwards - let topmost views consume scroll distance
			// first.
			for (int i = count - 1; i >= 0; i--)
			{
				// TODO: Add versioned support here for transformed views.
				// This will not work for transformed views in Honeycomb+
				final View child = group.getChildAt(i);
				if (x + scrollX >= child.getLeft() && x + scrollX < child.getRight() &&
					y + scrollY >= child.getTop() && y + scrollY < child.getBottom() &&
					canScroll(child, true, dx, x + scrollX - child.getLeft(),
								y + scrollY - child.getTop())) { return true; }
			}
		}

		return checkV && ViewCompat.canScrollHorizontally(v, -dx);
	}

	@Override
	public boolean dispatchKeyEvent(KeyEvent event)
	{
		// Let the focused view and/or our descendants get the key first
		return super.dispatchKeyEvent(event) || executeKeyEvent(event);
	}

	/**
	 * You can call this function yourself to have the scroll view perform
	 * scrolling from a key event, just as if the event had been dispatched to
	 * it by the view hierarchy.
	 * 
	 * @param event
	 *            The key event to execute.
	 * @return Return true if the event was handled, else false.
	 */
	public boolean executeKeyEvent(KeyEvent event)
	{
		boolean handled = false;
		if (event.getAction() == KeyEvent.ACTION_DOWN)
		{
			switch (event.getKeyCode())
			{
				case KeyEvent.KEYCODE_DPAD_LEFT:
					handled = arrowScroll(FOCUS_LEFT);
					break;
				case KeyEvent.KEYCODE_DPAD_RIGHT:
					handled = arrowScroll(FOCUS_RIGHT);
					break;
				case KeyEvent.KEYCODE_TAB:
					if (Build.VERSION.SDK_INT >= 11)
					{
						// The focus finder had a bug handling FOCUS_FORWARD and
						// FOCUS_BACKWARD
						// before Android 3.0. Ignore the tab key on those
						// devices.
						if (KeyEventCompat.hasNoModifiers(event))
						{
							handled = arrowScroll(FOCUS_FORWARD);
						}
						else if (KeyEventCompat.hasModifiers(event, KeyEvent.META_SHIFT_ON))
						{
							handled = arrowScroll(FOCUS_BACKWARD);
						}
					}
					break;
			}
		}
		return handled;
	}

	public boolean arrowScroll(int direction)
	{
		View currentFocused = findFocus();
		if (currentFocused == this) currentFocused = null;

		boolean handled = false;

		View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused,
																	direction);
		if (nextFocused != null && nextFocused != currentFocused)
		{
			if (direction == View.FOCUS_LEFT)
			{
				// If there is nothing to the left, or this is causing us to
				// jump to the right, then what we really want to do is page
				// left.
				if (currentFocused != null && nextFocused.getLeft() >= currentFocused.getLeft())
				{
					handled = pageLeft();
				}
				else
				{
					handled = nextFocused.requestFocus();
				}
			}
			else if (direction == View.FOCUS_RIGHT)
			{
				// If there is nothing to the right, or this is causing us to
				// jump to the left, then what we really want to do is page
				// right.
				if (currentFocused != null && nextFocused.getLeft() <= currentFocused.getLeft())
				{
					handled = pageRight();
				}
				else
				{
					handled = nextFocused.requestFocus();
				}
			}
		}
		else if (direction == FOCUS_LEFT || direction == FOCUS_BACKWARD)
		{
			// Trying to move left and nothing there; try to page.
			handled = pageLeft();
		}
		else if (direction == FOCUS_RIGHT || direction == FOCUS_FORWARD)
		{
			// Trying to move right and nothing there; try to page.
			handled = pageRight();
		}
		if (handled)
		{
			playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));
		}
		return handled;
	}

	boolean pageLeft()
	{
		if (mCurItem > 0)
		{
			setCurrentItem(mCurItem - 1, true);
			return true;
		}
		return false;
	}

	boolean pageRight()
	{
		if (mAdapter != null && mCurItem < (mAdapter.getCount() - 1))
		{
			setCurrentItem(mCurItem + 1, true);
			return true;
		}
		return false;
	}

	/**
	 * We only want the current page that is being shown to be focusable.
	 */
	@Override
	public void addFocusables(ArrayList<View> views, int direction, int focusableMode)
	{
		final int focusableCount = views.size();

		final int descendantFocusability = getDescendantFocusability();

		if (descendantFocusability != FOCUS_BLOCK_DESCENDANTS)
		{
			for (int i = 0; i < getChildCount(); i++)
			{
				final View child = getChildAt(i);
				if (child.getVisibility() == VISIBLE)
				{
					ItemInfo ii = infoForChild(child);
					if (ii != null && ii.position == mCurItem)
					{
						child.addFocusables(views, direction, focusableMode);
					}
				}
			}
		}

		// we add ourselves (if focusable) in all cases except for when we are
		// FOCUS_AFTER_DESCENDANTS and there are some descendants focusable.
		// this is
		// to avoid the focus search finding layouts when a more precise search
		// among the focusable children would be more interesting.
		if (descendantFocusability != FOCUS_AFTER_DESCENDANTS ||
			// No focusable descendants
			(focusableCount == views.size()))
		{
			// Note that we can't call the superclass here, because it will
			// add all views in. So we need to do the same thing View does.
			if (!isFocusable()) { return; }
			if ((focusableMode & FOCUSABLES_TOUCH_MODE) == FOCUSABLES_TOUCH_MODE &&
				isInTouchMode() && !isFocusableInTouchMode()) { return; }
			if (views != null)
			{
				views.add(this);
			}
		}
	}

	/**
	 * We only want the current page that is being shown to be touchable.
	 */
	@Override
	public void addTouchables(ArrayList<View> views)
	{
		// Note that we don't call super.addTouchables(), which means that
		// we don't call View.addTouchables(). This is okay because a ViewPager
		// is itself not touchable.
		for (int i = 0; i < getChildCount(); i++)
		{
			final View child = getChildAt(i);
			if (child.getVisibility() == VISIBLE)
			{
				ItemInfo ii = infoForChild(child);
				if (ii != null && ii.position == mCurItem)
				{
					child.addTouchables(views);
				}
			}
		}
	}

	/**
	 * We only want the current page that is being shown to be focusable.
	 */
	@Override
	protected boolean onRequestFocusInDescendants(int direction,
													Rect previouslyFocusedRect)
	{
		int index;
		int increment;
		int end;
		int count = getChildCount();
		if ((direction & FOCUS_FORWARD) != 0)
		{
			index = 0;
			increment = 1;
			end = count;
		}
		else
		{
			index = count - 1;
			increment = -1;
			end = -1;
		}
		for (int i = index; i != end; i += increment)
		{
			View child = getChildAt(i);
			if (child.getVisibility() == VISIBLE)
			{
				ItemInfo ii = infoForChild(child);
				if (ii != null && ii.position == mCurItem)
				{
					if (child.requestFocus(direction, previouslyFocusedRect)) { return true; }
				}
			}
		}
		return false;
	}

	@Override
	public boolean dispatchPopulateAccessibilityEvent(AccessibilityEvent event)
	{
		// ViewPagers should only report accessibility info for the current
		// page,
		// otherwise things get very confusing.

		// TODO: Should this note something about the paging container?

		final int childCount = getChildCount();
		for (int i = 0; i < childCount; i++)
		{
			final View child = getChildAt(i);
			if (child.getVisibility() == VISIBLE)
			{
				final ItemInfo ii = infoForChild(child);
				if (ii != null && ii.position == mCurItem &&
					child.dispatchPopulateAccessibilityEvent(event)) { return true; }
			}
		}

		return false;
	}

	@Override
	protected ViewGroup.LayoutParams generateDefaultLayoutParams()
	{
		return new LayoutParams();
	}

	@Override
	protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p)
	{
		return generateDefaultLayoutParams();
	}

	@Override
	protected boolean checkLayoutParams(ViewGroup.LayoutParams p)
	{
		return p instanceof LayoutParams && super.checkLayoutParams(p);
	}

	@Override
	public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs)
	{
		return new LayoutParams(getContext(), attrs);
	}

	private class PagerObserver extends DataSetObserver
	{
		@Override
		public void onChanged()
		{
			dataSetChanged();
		}

		@Override
		public void onInvalidated()
		{
			dataSetChanged();
		}
	}

	/**
	 * Layout parameters that should be supplied for views added to a ViewPager.
	 */
	public static class LayoutParams extends ViewGroup.LayoutParams
	{
		/**
		 * true if this view is a decoration on the pager itself and not a view
		 * supplied by the adapter.
		 */
		public boolean	isDecor;

		/**
		 * Where to position the view page within the overall ViewPager
		 * container; constants are defined in {@link Gravity}.
		 */
		public int		gravity;

		public LayoutParams() {
			super(FILL_PARENT, FILL_PARENT);
		}

		public LayoutParams(Context context, AttributeSet attrs) {
			super(context, attrs);

			final TypedArray a = context.obtainStyledAttributes(attrs, LAYOUT_ATTRS);
			gravity = a.getInteger(0, Gravity.NO_GRAVITY);
			a.recycle();
		}
	}
}
